Method and apparatus for protection of metallic surfaces



March 16 1926. 1,576,581

G. H. ELMORE ET AL METHOD AND APPARATUS FOR PROTECTION OF METALLICSURFACES Filed April 9. 1925 REVERSING SWITCH 8 a such conditionelectrolytic corrosion of the Patented Mar. 16, 1926.

UNITED STATES PATENT OFFICE.

GUY H. ELMORE AND HENRY J. CREIGHTON, OF SWARTHMORE, PENNSYLVANIA,

ASSIGNORS TO ANTISCALE CORPORATION,

CORPORATION OF DELAWARE.

OF PHILADELPHIA, PENNSYLVANIA, A

METHOD AND APPARATUS FOR PROTECTION OF METALLIC SURFACES.

Application filed April 9, 1925. Serial No. 21,772.

vT0 all whom it may concern:

-Be it known that we, GUY H. ELMORE and HENRY J. CREIGHTON, the formerbeing a citizen of the United States, and a resident of Swarthmore,county of Delaware, and State of Pennsylvania, and the latter being asubject of the King of Great Britain, an a citizen of the Dominion ofCanada, residing at Swarthmore, county of Delaware, and State ofPennsylvania, have invented certain new and useful Improvements inMethods and Apparatus for Protection of Metallic Surfaces, of which thefollowing is a specification.

Our invention relates to a method and apparatus for preventing oreliminating the scaling or encrusting of metal in contact with fluid, aspecial and important embodiment and application of our invention beingapparatus and a method whereby con tainers or conduits such as boilers,evaporators, economizers, condensers, cold and hot water pipes and thelike are protected against the formation of scale from sediment orprecipitates in the fluid therein contained and beingprocessed. I

The fact that scale or encrustation forms upon metallic surfaces thatare in contact with fluid, particularly when the fluid is undergoing achange of character or temper ature, is Well known and the fact thatunder metal takes place is also well known, such corrosion beinghereinafter referred to as normal or natural electrolytic corrosion, anexample thereof being the rusting or pitting of a steam boiler.

It has heretofore been proposed to protect a metallic surface that is incontact with a fluid against the formation of scale or encrustation bypassing an electric current through the metallic body of which thesurface is to be protected, or by introducing the current to themetallic body and withdrawing it from the fluid or vice versa. And, ithas been proposed heretofore to employ electric current of low voltage.In accordance with our invention we propose to introduce an electriccurrent to and withdraw it from the metallic body of which the surfaceis to be protected without directly introducing the current to orwithdrawing it from the liquid that is in contact with that surface. Wehave found that the prevention and elimination of the formation andadhesion of scale or encrustation upon the surface of the metallic bodythat is in contact with the fluid can not be prevented merely byregulation of the voltage of current that 'is passed through themetallic body; and we have found that protection of minals of a sourceof electric current are connected to remote points of the metallic bodof which the surface is to be protected ,agamst the formation andadhesion of scale and encrustation. The potential difference between thepoints at which the source is so connected is so regulated in accordanceWith our invention that the potential gradient, i. e., the ratio of thetotal potential difference between the points at which the source isconnected to the distance between those points, will be low enough thatthe natural or normal electrolytic corrosion of the surface will not beappreciably accelerated or augmented. If the surface to be protected isof such form that points widely spaced along that surface arenevertheless in such proximity that current might flow through the fluidbetween those two points, the points of the surface which are to beconnected with the terminals of the source of current are so selected asto avoid such straying or diversion of the current throu h the fluid.The value of the potential gra ient that may be maintained along theextent of the body of which' the surface is to be,

protected will vary with the conditions to whichthat surface issubjected. The conductivity of the fluid in contact with the surface tobe protected, the character of that fluid, for example, the chemicalactivity thereof with respect to the surface-to be protected, thetemperature of the surface to e protected, and the proximity of portionsof the surface are conditions that may control the value of thepotential gradient that must be employed and'the points at which thesource of current is to be connected thereto. In determining the properpotential gradient to be used," under the particular conditionssurrounding the surface to be protected, and the points at which thesource of electric current 1s to be connected to that surface, thecontrolling factor is that the normal or natural electrolytic corrosionshall not be appreciably augmented 0r.- accelerated beyond that whichwould take place if no electric current from an external source werepassed through the body 'of which the surface is to be protected. Wehave found that, in some cases at least, the potential gradient shouldbe lower with fluids of higher conductivity. The potential gradienthaving been ascertained the amount ofcurrent passin through the metallicbody of which the sur ace is to be protected is to be brought to suchvalue that formation and adhesion of scale or encrustation willordinarily be prevented and in most cases previously formed scale willbe removed. The amount of the current flowing through the body of whichthe surfaceis to be protected is not, in accordance with our invention,to be determined by a measurement of only the amount of current flowingbut is to be determined by ratio of that current to the cross-sectionalarea of the metallic body of which the surface is to be protected. Inother words it is the cross-sectional density of the current that is themeasure by which the amount of current is to be regulated. If it befound that with a given potential gradient a certain amount of currentwill protect the surface of a given metallic body the current necessaryto protect the surface of another metallic body of a similar metal underthe same conditions must be such that the cross-sectional density of thecurrent is substantially the same in both bodies.

Certain metallic bodies of which the surface is to be protected,\forexample, a steam boiler, have a current flowing in them that is producedby a thermo-electric or thermocouple efi'ect in. the metallic bodyitself, by reason of variations in the temperature and chemicalcomposition throughout the metallic body, or by galvanic action due tocontact of the metal with liquid or by some other cause, such a currentbeing herein referred to as inherent current. In order to insure theflow in those bodies of the necessary and effectivecross-sectionaldensity of current thedirection of flow is determined ofsuch inherent current, if any, between the points to which the terminalsof the external source of current are to be connected. The source ofcurrent is .then so' connected to those points that the currenttherefrom will flow in the metallicbody in the same direction as theinherent current. Otherwise, it may not be possible to produce withinthe metallic ody a sufiic'iently high cross-sectional density ,to effectthe desired result without the use of a potential gradient that willappreciably accelerate. or augment the natural or normal electrolyticcorrosion.

Having set forth a general rule whereby the potential gradient andcurrent value are to bedetermined, we set forth as a specific examplefor'the purpose of assisting in the practice of our invention, but withthe understanding that our invention is not limited thereto, ourobservation that in connection with a steam boiler using water of areaof metal and several hundred milliamperes per square foot thereof inorder that sufiicient current will flow to effect elimination ofencrustation.

troduced to or directly conducted out of the fluid that is in contactwith the surface to be protected. The potential gradient between thepoints of connection is brought down to or below a value that will notcause appreciable acceleration of the normal elect-rolytic corrosion of.the surface. We have found that thermo-coupl'es provide a convenientsource of current that will produce the desired potential gradientbetween points that are not too far removed from one another. Inaccordance with our invention the current is so regulated that the valueof the ratio of the current to the cross-sectional area of the body ofwhich the surface is. to be protected, 1. e., the cross-sectionalcurrent density, will be great enough to prevent the.

formation and adhesion of scale or encrustation, care being taken,however, that the inherent current, if any, flowing within the body byreason of its contact with the liquid, or for any other reason, does notnegative the effect of the current supplied from the external source,and care being taken that the potential gradient is not increased to avalue that will appreciably augment or accelerate the naturalelectrolytic corrosion of the surface to be protected.

It may be desirable to interrupt or reverse at various intervals theflow of current that is employed in the practice of our invention.

Understanding that we are not limited to any theory of the operation ofour invention, it is our belief that the prevention of the formation andadhesion of scale is effected in accordance with our invention byneutralization or reversal of ordinary electrolytic corrosion action andby the formation of gas whereby scale or encrustation is prevented fromforming and adhering. It may be, however, that the elimination of theformation of oxide or other compounds of the metal of the surface to beprotected or the reduction of such compounds prevents the formation andadhesion of scale or encrustation, the admixture of products ofelectrolytic corrosion with precipitates or sediment in the fluid duringthe formation of scale or encrustation tending possibly to cause orincrease the adhesion of the scale to the surface to be protected. Withthe same understanding but desiring to make full disclosure of ourinvention it is our belief that the flow of current through the body ofwhich a surface is to be protected, when properly regulated andcontrolled, effects protection of the surface as follows: The electronscoming from the negative pole of the source of electric current attractto metallic ['electro-positive] areas of that part of the surface of thecontainer that is in contact with the fluid that is being processedtherein, positive-charged hydrogen ions of the fluid that is beingprocessed, and those hydrogen ions take up electrons from such surfaceand are set free as hydrogen atoms. The consumption of electrons reducesthe flow of electrons to the positive pole of the source and negativelycharged hydroxyl ions. from the fluid that is being processed aretherefore attracted to an electro-negative area [e. g., an impure spotin the iron] and they discharge there and restore the flow of electrons.The discharged hydroxyl ions are incapable of separate existence anddecompose to form water and gaseous oxygen, The oxygen, or some part ofit, collecting between the container or conduit surface and any scalethereon will ultimately exert suflicient force to loosen the scale fromthe metallic surface. The hydrogen atoms produced when the hydrogen ionsare discharged, are consumed by the oxide of the metal of the containerthat has been formed [0. g., iron oxide]. The removal of the hydrogenfrom the liquid also prevents the accumulation of gaseous pressure ofthe hydrogen and permits the above described electrolytic action'toproceed at such low voltages as may, without destructive action on thecontainer, be employed. The removal of the hydrogen permits thecontinued separation in the fluid being processed of hydrogen ions andhydroxyl ions [i. e., dissociation of water] at the many places whereimpure and pure metal of the container are adjacent. The requirementthat the crossscctional density of the current shall have a certainvalue in accordance with our inven tion appears to indicate that in thetheory above set forth there must be a certain density of distributionof electrons over the surface to be protected and that such density ofdistribution is produced by maintaining the cross-sectional density ofthe current at the proper value. The theory above set forth appears torequire the presence of metallic oxide in order that removal of scale bygas pressure may proceed and thereby indicates the apparent desirabilityof an interruption of the current flow in order to permit the formationof sufficient oxide to produce, through its reduction, a necessaryamount of gas to remove scale where the removal of scale is the desiredend.

T o assist in the understanding of our invention we have showndiagrammatically in the single figure of the drawings, apparatusembodying and whereby our invention may be practised.

A boiler 1 is provided with the usaul steam outlet pipe 2. The junction3 of the thermo-couple is held in contact with the steam pipe 2 by meansof the collar 4, as a convenient means of heating the junction of thethermo-couple. The leads 5 and 5' of the thermo-couple conduct currentto the brushes 6 and 7 of a reversing device comprising a disk Dcomposed of conductive parts 8 and 9 separated by an insulating member10, the disk being mounted for rotation. Brush 11 that bears on the diskis connected to one end of the boiler at 12 by the lead 12 and brush 13is connected through a variable resistance 14 to the other end of theboiler at 15 by means of the lead 15'. The disk D may be continuously orintermittently rotated in order to effect a reversal of the flow withinthe body to be'protected of externally supplied current, or, if there isa flow of current within the body to be protected by reason of itscontact with the liquid, for example, from the point 12 to the point 15or vice versa, the disk D may be rotated to a position that will causethe current from the themo-couple 3,

or other source of current, to flow throu h the boiler 1 or other bodyto be protected 1n the same direction as the current therein that is dueto its contact with the liquid. It is to be understood that withdifferent forms of boilers or other bodies of which the surface is to beprotected, the points at which the source of current are connected maybe varied in accordance with the principles set forth herein and thesource of current may be other than a thermo-couple or it may be aplurality of thermo-couples connected in such a way as to meet therequirements of our invention as herein set forth.

What we claim and desire to secure by Letters Patent of the UnitedStates is:

1. The process of protecting a surface of ametallic body againstencrustation or scaling which comprises passing an electric cur-.

rent through the body and maintaining throughout the body of which thesurface is to be protected a potential gradient below that which willaccelerate normal electrolytic corrosion thereof while maintaining across sectional density of current in the body whereby encrustation andscaling of the surface will be eliminated.

2. The process of protecting a surface of a metallic body againstencrustation or scaling which comprises passing an electric currentthrough the body and maintaining throughout the body ofwhich the surfaceis to be protected a potential gradient below that which will acceleratenormal elec-- trolytic corrosion thereof while causing the currentflowing through the body .to be of such strength as to" eliminatescaling and encrustation of the surface;

3. The process of protecting a surface of a metallic body againstencrustation or scaling which comprises maintaining the flow of anelectric current through the body of such strength as to eliminatescaling and encrustatlon ofthe surface whlle malntaining the voltage ofthe current below that which,

will augment or accelerate the normal electrolytlc corrosion of thesurface to be pro-v tected beyond what would occur in the absence of thecurrent so body.

1. The process of protecting a surface of a passed through the metallicbody against encrustation or scaling which comprises connecting theterminals of a source of electric current directly to spaced points ofthe body, regulating the current flowing in the circuit so fornied andthereby eliminating scaling and encrustation of the surface whilemaintaining the otential difference between said points 0 connectionbelow that which will augment or accelerate the natural corrosion of thesurface to be protected beyond what would occur in the absence of thecircuit so formed.

" 5. The process of protecting a liq'uid-contactmg surface of a metallicbody against necting the terminals of a source of electric current tospaced points of said body and thereby completing an electric circuitincluding apart of said body, so regulating" the direction of currentflowing from said source that current from said source produces in saidbody between said points a flow of current in the same direction as theinherent current in said body, and regulating the current between saidpoints and thereby eliminating scaling and encrustation,

6. The process of protecting a liquid-contacting surface of a metallicbody against encrustation or scaling which comprises connecting theterminals of a source of electric current to spaced points of said bodyand thereby completing an electric circuit including a part of saidbody, so regulating the direction of current flowing from said sourcethat current from said source produces in said body between said pointsa flow of current in the same direction as the in herent current in saidbody, and regulating the current between said points and therebyeliminating scalingand encrustation while maintaining the potentialgradient between said points below that which will accelerate normalelectrolytic corrosion of thesurface.

7. The process of'protecting a liquid-contacting surface of a metallicbody against encrustation or scaling which comprises connecting theterminals of a source of electric surface of a metallic body, a sourceof current,'electrical connections between the respective terminals ofsaid source and remotely spaced points of the body of which the surfaceis to be protected, said connections including a variable resistance andpolarity reversing means.

9. In combination with a steam boiler, thermoelectric means, thejunction of which is heated byheat from the boiler and connectionsbetween the respective terminals of said thermo-electric means andspaced points of the boiler, said connections including a variableresistance and polarity reverslng means.

10. The process of protecting against encrustation or scaling a surfaceof a metallic body in contact with liqiiid, which comprises passing anelectric current throughthe body between spaced points thereof andmainand intermittently reversing the direction taining in the bodybetween said points a of current flow between said points atsuitpotential gradient below that which will acable frequency. 10cel'erate normal electrolytic corrosion there- In testimony whereof, wehave signed our 5 of while causing the current flowing through names tothis specification.

the body to be of such strength as to elimi- GUY H. ELMORE.

nate scaling and encrustation of the surface HENRY J. CREIGHTON.

